1. Field of the Invention
The present invention relates in general to integrated circuit (IC) manufacturing. More specifically, it relates to methods in IC manufacturing processes for using data regarding manufacturing procedures IC's have undergone, such as repair procedures, to select procedures the IC's will undergo, such as additional repair procedures.
2. State of the Art
As shown in FIG. 1, a typical process 10 for manufacturing very small electronic circuits referred to as “Integrated Circuits” (IC's) begins with the IC's being formed or “fabricated” on the surface of a wafer 12 of semiconductor material, such as silicon. Once fabricated, IC's are electronically probed to determine whether they are functional (i.e., “good”) or nonfunctional (i.e., “bad”). If any IC's are found to be bad, an attempt is made to repair those IC's by replacing nonfunctional circuit elements in the IC's with spare circuit elements. For example, Dynamic Random Access Memory (DRAM) IC's are typically repaired by replacing nonfunctional rows or columns of memory cells in the IC's with spare rows or columns.
These repairs are not always successful, because the number of spare circuit elements on an IC may be exhausted before all nonfunctional circuit elements on the IC are replaced, and because some circuit elements on IC's have no spares to replace them. As a result, a number of bad IC's typically remain on a wafer 12 even after attempts are made to repair the IC's. The location of bad IC's on a wafer 12, along with the location of any good IC's on the wafer 12, is typically stored in a computer database commonly referred to as a “wafer map.”
After being probed and, if necessary, repaired, IC's begin an assembly process with their wafer 12 being mounted on an adhesive film. In some instances, the film is a special high-adhesion Ultraviolet (U.V.) film. Without cutting the adhesive film, IC's are sawed from their wafer 12 into discrete IC dice or “chips” using high-speed precision dicing equipment. IC dice mounted on U.V. film are then exposed to U.V. light to loosen the grip of the film on the dice. IC dice identified as good by their wafer map are then each “picked” by automated equipment from their sawed wafer 12 and its associated film and “placed” on an epoxy coated bonding site of one lead frame in a strip of interconnected lead frames, while IC dice identified as bad are discarded into a scrap bin 14. The epoxy attaching the good IC dice to their lead frames is then cured, and the attached dice are wire bonded to their lead frames using high speed bonding equipment.
Once wire bonded, IC dice and their associated lead frames are formed into IC packages using a hot thermosetting plastic encapsulant injected into a mold. IC packages are then cured to set their plastic encapsulant. After encapsulation and curing, leads of the lead frames projecting from the packages are dipped in a cleansing chemical bath in a process referred to as “de-flash” and then electroplated with a lead/tin finish. Connections between lead frames in lead frame strips are then cut to “singulate” IC packages into discrete IC devices.
After assembly, discrete IC devices are tested in a simple electronic test referred to as an “opens/shorts” test, which checks for “opens” (i.e., no connection) within the devices where connections should exist and “shorts” (i.e., a connection) where connections should not exist. Devices that pass the opens/shorts test proceed on through the process 10 to various burn-in and test procedures where they are tested for functionality, operability, and reliability, and devices that pass these burn-in and test procedures are then typically shipped to customers.
IC devices that fail any of the opens/shorts, burn-in, and test procedures are checked to determine whether they are repairable. This “check” typically includes an electronic “querying” of a device to determine whether enough spare circuit elements remain in the device to effect necessary repairs. Devices determined to be unrepairable are scrapped in a scrap bin 16, while devices that are repairable are repaired, typically by replacing nonfunctional circuit elements in the devices with spare circuit elements in the same manner as described above. After being repaired, these devices then reenter the manufacturing process 10 just prior to the opens/shorts, burn-in, or test procedures they failed.
Electronic querying of IC devices to determine whether spare circuit elements are available to effect repairs increases the time required to move the devices through the manufacturing process 10 and places an additional burden on expensive testing resources. While the extra time added by querying one IC device may be insignificant, the time required to query thousands and thousands of IC devices adds up and can result in a significant reduction in the number of IC devices completing the manufacturing process 10 in a given amount of time. Therefore, there is a need in the art for a method of determining whether enough spare circuit elements are available in an IC device to effect repairs without having to query the device.
Similarly, as shown in FIG. 2, a typical process 20 for manufacturing so-called “flip-chip” and “Chip-On-Board” (COB) Multi-Chip Modules (MCM's), in which multiple IC dice are typically attached directly to a substrate, such as a printed circuit board (PCB), begins with IC's being fabricated on the surface of a semiconductor wafer 22 in the same manner as described above. Once fabricated, IC's are electronically probed to determine whether they are good or bad, and if any IC's are found to be bad, an attempt is made to repair those IC's (i.e., make them good IC's) by replacing nonfunctional circuit elements in the IC's with spare circuit elements. The locations of good and bad IC's on a wafer 22 are then typically stored in an electronic wafer map.
After being probed and, if necessary, repaired, IC's begin an assembly process with their wafer 22 being mounted on an adhesive film. Without cutting this film, IC's are then sawed from their wafer 22 into discrete IC dice using high-speed precision dicing equipment. IC dice that are mounted on the special high-adhesion U.V. film described above are then exposed to U.V. light to loosen the grip of the film on the dice.
IC dice identified as good by their electronic wafer map are then each picked by automated equipment from their sawed wafer 22 and its associated film, typically for attachment to a substrate in a panel of multiple substrates, such as a panel of interconnected PCB's. If the assembly process is a flip-chip process, picked dice are then flipped and directly attached at their active, front side surfaces to substrates to form MCM's. If the assembly process is a COB process, picked dice are directly attached at their inactive, back side surfaces to adhesive coated bonding sites of substrates to form MCM's. IC dice identified as bad are discarded into a scrap bin 24.
Panels of MCM's are then cured. If the assembly process is a COB process, the MCM's may be plasma cleaned, if necessary, and the COB IC dice are then wire bonded to their substrates using high speed bonding equipment.
After assembly, panels of MCM's are tested in an opens/shorts test. Panels having COB IC dice that pass the opens/shorts test proceed on through the manufacturing process 20 so the dice can be encapsulated using an overmold, hard cover, or so-called “glob” top, while panels having flip-chip IC dice that pass the opens/shorts test may have their dice encapsulated using an underfill followed by an overmold, hard cover, or glob top. As will be described in more detail below, alternatively flip-chip IC dice may be encapsulated after burn-in and test procedures. The disposition of panels of MCM's having COB and flip-chip attached IC dice that fail the opens/shorts test will be described in more detail below.
Panels of MCM's having both COB and flip-chip IC dice, including those panels having flip-chip IC dice that were not encapsulated, are then singulated into discrete MCM's, typically by a shear press or router. After singulation, those MCM's having encapsulated IC dice have their dice tested again in an additional opens/shorts test to check for problems caused by the encapsulation. MCM's having encapsulated dice that pass this additional opens/shorts test, as well as MCM's having dice that were not encapsulated, then proceed on in the manufacturing process 20 to various burn-in and test procedures. The disposition of any MCM's having encapsulated dice that fail the additional opens/shorts test will be described in more detail below.
After the burn-in and test procedures, MCM's having unencapsulated flip-chip IC dice that pass the procedures proceed on in the process 20 so their dice may be covered with an overmold, hardcover, or glob top. Dice covered in this manner are then checked in a further opens/shorts test for problems caused by their being covered, and MCM's having dice that pass this further test are then typically shipped to customers. MCM's having encapsulated IC dice that pass the burn-in and test procedures skip this final opens/shorts test and typically proceed to shipping.
MCM's having attached IC dice that fail any of the opens/shorts, burn-in, and test procedures are checked to determine whether their associated IC dice are repairable. This “check” typically includes an electronic querying of the IC dice to determine whether enough spare circuit elements remain in the dice for effecting repairs. MCM's determined to have unrepairable IC dice are then either reworked using replacement IC dice in an expensive and time-consuming procedure or scrapped in a scrap bin 26, while MCM's having IC dice that are repairable are repaired, typically by replacing nonfunctional circuit elements in the IC dice with spare circuit elements. After being repaired, these MCM's then reenter the manufacturing process 20 just prior to the opens/shorts, burn-in, or test procedures they failed.
As discussed above, electronic querying of IC dice to determine whether spare circuit elements are available to effect repairs increases the time required to move MCM's through the manufacturing process 20 and places an additional burden on expensive testing resources. Also, IC dice that require repair, and are found to be unrepairable only after the assembly process, waste assembly time, materials, and resources and necessitate the scrapping or reworking of MCM's that may contain many functional dice. It is desirable, then, to have an IC manufacturing method for identifying unrepairable IC dice so they may be kept out of COB, flip-chip, and other MCM assembly processes.
As described in U.S. Pat. No.'s 5,301,143, 5,294,812, and 5,103,166, some methods have been devised to electronically identify IC dice. Such methods take place “off” the manufacturing line, and involve the use of electrically retrievable identification (ID) codes, such as so-called “fuse ID's,” programmed into individual IC dice to identify the dice. The programming of a fuse ID typically involves selectively blowing an arrangement of fuses or anti-fuses in an IC die using electric current or a laser so that when the fuses or anti-fuses are accessed, they output a preprogrammed ID code. Unfortunately, none of these methods addresses the problem of identifying unrepairable IC dice “on” a manufacturing line.